MOS redistribution CCF #75 was released on July 29, 2010,
and I have already done the analysis with version #74, do I need
to care?

Only if you are doing spectral analysis of MOS data from observations
performed in 2010, or, for reasons difficult for us to figure
out, you analysed earlier observations using "cifbuild" with
the parameter "observationdate" set to later than January 1, 2010,

A formal error affects the value of the keyword EVALDATE in the header
of the MOS redistribution CCF files: "EMOS1_REDIST_0074.CCF" and
"EMOS2_REDIST_0074.CCF". This keyword, indicating the end of the CCF
constituent validity period, was erroneously set to January 1, 2010.
Consequently, the Calibration Index File (CIF) generated by "cifbuild"
for observations, whose start date is later than January 1, 2010,
incorrectly points to old versions of the redistribution CCF files. This
may potentially lead to inaccuracies in the spectral fitting.

Corrected CCF files are publicly available since July 29, 2010:
"EMOS1_REDIST_0075.CCF", and "EMOS2_REDIST_0075.CCF", whose
EVALDATE keyword value has been amended. Users are recommended to
update their CCF repository, regenerate the CIF, and then the
MOS redistribution matrices via "rmfgen".

The SOC produced MOS "canned" redistribution matrices are correct,
so they don't need to be re-generated, they are available from the
calibration web portal: